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John Moody July 13, 2009 Page 2 Bottom and Side slope Liner In line with previous landfill reviews over the last couple of years, DWR recommends that only reinforced geosynthetic clay liner (GCL) be used as park of the bottom and side slope liners underlying refuse. Waste Strength The strength assumed for the waste (friction angle — 33 degrees, cohesion — 100 psf) is slightly outside the range that DWR has recommended in the past. This is unconservative. Liner Strength The GCUHDPE liner strengths vary for the different modules. Except for Module 4, the existing modules seem to have a friction angle of 10 degrees and use a smooth HDPE or single-side textured geotextile. Module 4 and the proposed modules seem to have a friction angle of 12 degrees and use double-side textured HDPE geotextile. Cross section 1-1 includes a short section of smooth geomembrane — soil interface that is modeled using a friction angle of 17 degrees. The value of 17 degrees does not seem to be discussed in other portions of the report. The value appears too high and unconservative. Testing should reflect the range of stresses to be encountered. Based on the proposed height of the landfill, maximum stresses will be on the order of 20,000 psf. Because failure envelopes of liner interfaces are actually curvilinear and flatten out at high stresses, it is important to consider strength tests at the maximum stresses. Current testing seems to be limited to 10,000 psf or less. Note 2 of Appendix E, Geotechnical Analyses for the Vertical Expansion of North County Recycling Center and Sanitary Landfill, indicates a friction angle of 13 degrees. I believe this should be 12 degrees. Seismic Hazard Report Attachment C of Appendix E, Geotechnical Analyses for the Vertical Expansion of North County Recycling Center and Sanitary Landfill, contains the estimate of the MPE ground motions for the North County Site by Dr. Norman Abrahamson dated June 18, 2007.